Lazy Girl Spinach and Cheese Casserole

Spinach- 20 ounces cooked (usually in 2 10 ounce packages).

Greek Yogurt (as low carb as possible, can sub in sour cream)- 2 cups.

Dry Onion Soup Package (the stuff used in dips for example)- 2 cups.

Shredded or grated Cheese- 1 cup plus additional (as needed) for topping. I use cheddar for the casserole and a white cheese such as mozzarella and/or parmesan (combining is fun) for the topping.

Egg- 1 whipped.